Semiconductor devices have been utilized as temperature transducers for circuit applications in the past. Quite often transistor is connected in common emitter configuration between a supply voltage and ground to provide a reference voltage input to an operational amplifier. Since the operating characteristics of the transistor change or drift with ambient temperature, the transistor can be used as a temperature transducer.
The temperature coefficient, the number in millivolts per degrees centigrade, describes the response of the transistor with temperature. Because of the state of present day semiconductor technology, this response curve is rather linear over a broad range of temperatures. The temperature coefficient number, therefore, defines the slope of the output curve of a transistor with changes in ambient temperature.
Individual temperature coefficients tend to vary with individual transistors. Because of this fact, when a temperature sensing circuit using a transistor temperature transducer was to be produced in any quantity a manufacturer has had to select specially-grown, specially-selected matched transistors having the same temperature coefficient. This is an expensive procedure and it substantially raises the manufacturing costs of the circuit.
It is desirable, therefore, to provide a transistor, temperature transducer circuit which can use less expensive transistors having temperature coefficient values which may vary from individual transistor to transistor. Such a circuit should be able to be calibrated to a desired temperature coefficient preferably with a single adjustment.
An objective of this invention is to provide a temperature transducer circuit, using a transistor as the temperature sensing component, having a variable slope response curve.
A second objective of this invention is to provide a transistor, temperature transducer circuit having a single adjustment for calibrating the circuit to a specific slope or response curve.
A further objective of this invention is to include a single adjustable component adjacent to the temperature sensing transistor.
An even further objective of this invention is to provide a single adjustable component for adjusting the voltage reference point of the circuit.